1. Field of the Invention
The present invention relates to tin alloys for recording media. More particularly, it relates to a tin-lead alloy and a tin-copper alloy for recording media.
2. Description of the Prior Art
In recent years, there have been active research and development activities for high density large capacity information recording medium discs useful for a high speed random access system. In particular, research is being made for novel recording media which are capable of recording and reproducing information by irradiation of laser beam spots and which are provided with a suitable auxiliary means whereby recorded information can be erased and rewritten with new information.
Various recording media so far proposed for the recording and reproduction of information by means of laser beams, may generally be classified into such categories as a pit-forming type, a bubble-forming type, a magneto-optical type, and a phase transformation type (i.e. a thermal transformation type wherein the transmission, reflection, absorption, etc. of light is changed by the thermal energy) based on the type of a physical change caused to the recording medium by the thermal action of the spots of laser beams to record information.
Among such various types of recording media, those belonging to the phase transformation type are considered to be of particular interest for the possibility that the recorded information can be erased. As the recording media of this type, there have been proposed recording media wherein a thin layer of a composition of a variety of combination of germanium, tellurium, antimony, silicon, arsenic, bismuth, indium, gallium, thallium, selenium and sulfur, or a thin layer of a lower oxide (such as a mixture of Te and TeO.sub.2) is employed. However, in such conventional recording media wherein a thin layer of a composition of various combinations of chalcogenide substances or a thin layer of a lower oxide (such as a mixture of Te and TeO.sub.2) is used, the optimum beam intensity (i.e. a laser beam intensity sufficient to cause the phase transformation to the recording medium, whereby the secondary harmonic distortion in the reproduced signal from the portion of the recording medium irradiated with the laser beams of that intensity, is minimized) and/or the signal to noise ratio (S/N) varies considerably depending on the proportional ranges of the substances constituting the thin layer of the recording medium. Therefore, such conventional recording media had difficulty in that mass production of recording media having predetermined properties was not readily feasible.